The present invention relates generally to radio communications apparatus and, more particularly, to an apparatus that may both receive and transmit radio frequency ("RF") signals and that can scan a plurality of channels over a predetermined sequence.
Such mobile transceivers, including, for example, land-based mobile radios, often include a memory that may be loaded with a predetermined sequence, or "listing," of specific channels. Such mobile transceivers generally include a main unit, microphone, and hookswitch. The main unit may be mounted, for example, onto a dashboard of an automotive vehicle. It receives and processes RF signals to give an audible signal to the transceiver operator.
The microphone includes a push-to-talk ("PTT") button. When depressed, a sound signal received by the microphone may be converted to an electrical signal and sent to the main unit to be transmitted over a particular channel.
The hook physically holds the microphone in a predetermined position when not in use, such as, for example, on the side of the main unit. When in the condition of being in the predetermined position, the microphone is described as being "on hook." Conversely, when detached, the microphone is described as being "off hook." A typical transceiver may be adjusted to work in either manual or scan mode. While in manual mode, the operator may easily select a particular channel in the transceiver memory or, alternatively, may select any other channel within the range of the transceiver. It will then process RF signals received on a selected channel and broadcast them over a speaker to the transceiver operator. Similarly, the operator may take the microphone off hook, press the PTT button, and transmit a message over the selected channel.
While in scan mode, the transceiver may serially scan from one channel to another, according to a predetermined sequence in memory and note any channel activity (signals received over the selected channel). If no signal is received over a predetermined period of time (such as 0.04 to 0.40 seconds) the transceiver will move to the next channel, according to the predetermined serial sequence of channels in memory.
While the transceiver remains in scan mode, the operation of moving from one specific channel to another continues until an RF signal is detected on a particular channel. The scanning then is temporarily discontinued, and the transceiver monitors the active channel. If activity stops on the predetermined channel, the transceiver begins again the scanning operation, moving to the next predetermined channel, according to the chosen sequence in memory.
Typically, the scanning procedure continues only when the microphone transceiver is on hook. Current commercial mobile transceivers discontinue scanning when the microphone is taken off hook, in preparation for the operator beginning to transmit.
Most mobile transceiver systems utilize a priority scanning system in which one specific channel is "prioritized" over other channels. With such systems, the normal scanning procedure only continues when the microphone is on hook and there is no activity on the priority channel. Whenever the microphone is taken off hook or there is activity on the priority channel, scanning stops, and the transceiver switches to the priority channel. The operator may then monitor the priority channel and, if there is no activity on the channel, transmit over the priority channel.
Such transceivers include limitations that are poorly suited to meet the needs of many mobile transceiver operators, particularly those driving vehicles. Often, for example, a transceiver operator may hear an audio message while the transceiver is in scan mode and wish to transmit a response on the same channel.
The operator must then reach to the main unit to take the microphone off hook. If the transceiver has reverted to the priority channel, he or she must then use a manual input device on the main unit to select the channel he or she believes the last transmission was made on. Such operations are cumbersome, especially while driving and particularly when driving an emergency vehicle in response to a call for assistance. In such cases, the driver's attention may be focused elsewhere than on the efforts to manually select a channel on a transceiver.
Overcoming such limitations by simply allowing the operator to transmit by pushing the PTT button during the scanning operation would cause great difficulties. For proper operation of a transceiver, an operator should monitor a particular channel before he or she transmits on it. Allowing an operator to transmit during the scanning process might result in transmissions on random channels, dependent only on what channel the transceiver happened to be locked onto during the scanning process. Such a procedure would not allow the operator to monitor a channel before transmitting on it. Moreover, in many instances, the operator may wish to transmit over the priority channel quickly without reaching to the main unit to adjust the manual controls or waiting for the transceiver to scan to priority channel.